Field of the Invention
The present invention is directed to a screw-in type myocardial pacemaker lead, and in particular to such a lead having a steroid or steroid-based drug stored therein and means for dispensing the drug into tissue surrounding the distal end of the lead after implantation.
Various types of pacemaking leads and cardiopulmonary catheter structures are known in the art which include means for introducing a drug into the area surrounding tissue adjacent a distal end of the lead or catheter.
Catheters for drug delivery to an in vivo site with the catheter having a distal end designed to penetrate the heart wall, so that the distal end may be disposed within the heart, are described in U.S. Pat. No. 3,680,544, to Shinnick et al., and in U.S. Pat. No. 3,568,660, to Crites et al. Such catheters are primarily for use in emergency situations for introducing an externally administered drug into direct contact with the cardiac muscle, such as upon the occurrence of complete loss of cardiac output. As such, they do not include structure for storing the drug.
A combination pacing lead and drug delivery structure is disclosed in U.S. Pat. No. 4,360,031, to White. The lead disclosed in White has conventional electrical conductors for delivering pacing pulses to the heart, and also contains a channel, concentric with the conductor, through which a drug can be dispensed which exits through holes at the extreme distal end of the lead. The drug is contained within an implanted bladder, remote from the distal end of the lead, which can be filled by a percutaneous syringe.
Pacing leads which are anchored in the heart by means of tines at a distal end thereof which engage the trabeculae, and which have a cavity at the distal end of the lead in which a drug to counter undesirable interactions between the lead and tissue is contained, are disclosed in U.S. Pat. No. 4,711,251, to Stokes, and in U.S. Pat. No. 4,506,680, also to Stokes. Tined leads having tips consisting of porous or molecular sieve-forming material, with a drug being stored in and dispensed from the tip, are disclosed in U.S. Pat. No. 4,819,662, to Heil, Jr. et al.; in U.S. Pat. No. 4,606,118, to Cannon et al.; and in U.S. Pat. No. 4,577,642, to Stokes.
An epicardial lead is disclosed in U.S. Statutory Invention Registration No. H356, to Stokes et al., which lead has a barbed electrode tip with an axial bore therein. The bore, which terminates short of the tip, may have an inflammation-preventing drug stored therein. The drug is dispensed to surrounding tissue via a plurality of radial openings in the electrode, and is not dispensed directly at the electrode tip. Another epicardial drug eluting lead is described in the article "Preliminary Studies on a New Steroid Eluting Epicardial Electrode," Stokes, PACE, Vol. 11, pp. 1797-1803 (Nov. 1988), in the form of a helical screw-in electrode, with the lead having steroid contained in solid form located in the housing at the distal end of the lead. It is necessary for fluid to migrate into the distal end of the electrode through a porous channel to dissolve the steroid to permit the steroid to diffuse into the electrode-tissue interface.
An endocardial screw-in lead is disclosed in U.S. Pat. No. 4,876,109, to Mayer et al., which lead has having a biocompatible covering which is soluble in body fluids surrounding the fixation helix. The covering is for the purpose of shielding the helix during insertion of the lead, so that a mechanism does not have to be used to extend the helix from the distal end of the lead after insertion. Although the covering dissolves in body fluids after implantation, the covering material is not intended to therapeutically interact with the tissue.
A further screw-in pacemaker lead is disclosed in U.S. Pat. No. 4,819,661, to Heil, Jr. et al., which has a chamber open to the distal end of the lead with a matrix impregnated with a therapeutic drug being retained in the chamber.